研究 GPR 的直接波和反射波

IF 1.1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Near Surface Geophysics Pub Date : 2024-03-07 DOI:10.1002/nsg.12292
Eleni Tokmaktsi, Nectaria Diamanti, Georgios Vargemezis, Antonios Giannopoulos, A. Peter Annan
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引用次数: 0

摘要

在典型的探地雷达(GPR)勘测过程中,由于发射器和接收器(分别为 Tx 和 Rx)距离很近,Tx 产生的强大信号在不同的时间延迟后被 Rx 记录,在早期可能会饱和(即到达 Rx 的直接波(DW)信号)。这往往会造成浅层目标的掩蔽,使数据解读变得复杂。在这项研究中,我们的目的是检查 Tx 周围电磁信号的空间分布,试图找出 DW 信号变为最小值的区域,而来自地下目标的信号强度(即反射波 - RW)在理想情况下保持不变。DW 信号中这些局部最小值的位置可能会产生有利的 Tx-Rx 配置,在这种配置下,可以获得来自浅层地下目标的清晰反射波,而 DW 的参与则尽可能少。为了进行这样的研究,我们对平躺的反射器进行了静态现场测量,并在发射天线周围以反射、共偏移模式进行了数值模拟。在现场,我们还收集了广角反射-折射数据,以确定最上层的 GPR 波速。GPR 信号由 Rx 围绕 Tx 以三个不同半径的同心圆(即改变 Tx/Rx 间距)记录,每次使用特定的角度步长并改变 Tx/Rx 极化。合成数据使用三维有限差分时域建模工具生成。对现场数据和数值模拟数据进行了分析和比较,以研究在改变 Tx/Rx 距离、各自的角度位置以及相对极化/方位时,Tx 周围的 DW 和 RW 事件的表现。
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Studying GPR's direct and reflected waves
As the transmitter and receiver (Tx and Rx, respectively) are located in close proximity during a typical ground-penetrating radar (GPR) survey, the powerful signal generated by the Tx and which is then recorded by the Rx at various time delays, can be saturated at early times (i.e., this is the direct wave (DW) signal reaching the Rx). This often causes the masking of shallow targets, complicating data interpretation. In this study, our aim is to examine the spatial distribution of the electromagnetic signals around the Tx, attempting to locate areas where the DW becomes minimum, whereas the signal strength from subsurface targets (i.e., reflected wave – RW) remains ideally unchanged. The position of these local minima in the DW signal could give rise to advantageous Tx–Rx configurations, where clear reflections from subsurface targets lying at shallow depths can be obtained with the least possible involvement of the DW. To perform such a study, we carried out static field measurements over a flat lying reflector as well as numerical simulations in a reflection, common-offset mode around a transmitting antenna. In the field, we also collected wide-angle reflection–refraction data to determine the GPR wave velocity in the uppermost layer. GPR signals were recorded by the Rx around the Tx in three concentric circles of various radii (i.e., varying the Tx/Rx separation), using a specific angular step and varying the Tx/Rx polarization each time. The synthetic data were produced using a three-dimensional finite-difference time-domain modelling tool. Field and numerically simulated data were analysed and compared to study the behaviour of both the DW and RW events around the Tx when changing the Tx/Rx distance, their respective angular position, as well as their relative polarization/orientation.
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来源期刊
Near Surface Geophysics
Near Surface Geophysics 地学-地球化学与地球物理
CiteScore
3.60
自引率
12.50%
发文量
42
审稿时长
6-12 weeks
期刊介绍: Near Surface Geophysics is an international journal for the publication of research and development in geophysics applied to near surface. It places emphasis on geological, hydrogeological, geotechnical, environmental, engineering, mining, archaeological, agricultural and other applications of geophysics as well as physical soil and rock properties. Geophysical and geoscientific case histories with innovative use of geophysical techniques are welcome, which may include improvements on instrumentation, measurements, data acquisition and processing, modelling, inversion, interpretation, project management and multidisciplinary use. The papers should also be understandable to those who use geophysical data but are not necessarily geophysicists.
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